[Django] #35582: Refactors error messages in the `_dec` method to use f-strings instead of the older `%` formatting method. F-strings are more readable and modern

[Django]

#35582: Refactors error messages in the `_dec` method to use f-strings instead of
the older `%` formatting method. F-strings are more readable and modern
-------------------------------------+-------------------------------------
Reporter: Siam3h | Owner: Siam3h
Type: | Status: assigned
Cleanup/optimization |
Component: Utilities | Version: 5.1
Severity: Normal | Keywords: f-strings, code
Triage Stage: | readability
Unreviewed | Has patch: 0
Needs documentation: 0 | Needs tests: 0
Patch needs improvement: 0 | Easy pickings: 0
UI/UX: 0 |
-------------------------------------+-------------------------------------
** Description

This pull request refactors error messages in the `_dec` method to use
f-strings instead of the older `%` formatting method. F-strings are more
readable and modern, improving the overall code quality and consistency.

** Changes Made
- Converted string formatting in error messages to use f-strings.
- Enhanced readability of error messages.

** Benefits
- Improved readability and maintainability of the code.
- Consistency with modern Python practices.

**Testing
- Ran existing tests to ensure no functionality is broken.
--
Ticket URL: <https://code.djangoproject.com/ticket/35582>
Django <https://code.djangoproject.com/>
The Web framework for perfectionists with deadlines.